Conversion error

Hello. I am a new user of the video converter. Every time I convert I get on error after the conversion finishes, that says something similar to the following (see log entry below)....I then says that the conversion failed and asks if I would like to convert again...however the file still appears to be converted and plays. Anyone know why I get this? I am converting to MP4 and I have tried different source file types, webm, mp4, flv, etc.